The process of fermentation production of chemical products using sugars as raw materials has been used for producing various industrial materials. At present, as the sugars to be used as fermentation feedstocks, those derived from food materials such as sugar cane, starch and sugar beet are industrially used. However, in view of the fact that rise in the prices of food materials is expected due to future increase in the world population, or in an ethical view of the fact that sugars as industrial materials may compete with sugars for food, a process for efficiently producing a sugar liquid from a renewable nonfood resource, that is, cellulose-containing biomass, or a process for efficiently converting an obtained sugar liquid as a fermentation feedstock to an industrial material needs to be constructed in the future.
Examples of disclosed methods for producing a sugar liquid from a cellulose-containing biomass include methods for producing sugar liquids using sulfuric acid, such as methods for producing sugar liquids by acid hydrolysis of cellulose and hemicellulose using concentrated sulfuric acid (Japanese Translated PCT Patent Application Laid-open No. 11-506934 and JP 2005-229821 A) and a method wherein a cellulose-containing biomass is subjected to hydrolysis treatment using dilute sulfuric acid and then enzymatically treated with cellulase and the like to produce a sugar liquid (A. Aden et al., “Lignocellulosic Biomass to Ethanol Process Design and Economics Utilizing Co-Current Dilute Acid Prehydrolysis and Enzymatic Hydrolysis for Corn Stover,” NREL Technical Report (2002)).
Further, examples of disclosed methods in which acids are not used include a method wherein a cellulose-containing biomass is hydrolyzed using subcritical water at about 250 to 500° C. to produce a sugar liquid (JP 2003-212888 A), a method wherein a cellulose-containing biomass is subjected to subcritical water treatment and then enzymatically treated to produce a sugar liquid (JP 2001-95594 A), and a method wherein a cellulose-containing biomass is subjected to hydrolysis treatment with pressurized hot water at 240° C. to 280° C. and then enzymatically treated to produce a sugar liquid (JP 3041380 B).
However, during the hydrolysis of a cellulose-containing biomass, at the same time with decomposition of the cellulose or hemicellulose component or the like, decomposition reaction of produced sugars such as glucose and xylose proceeds, and by-products such as furan compounds including furfural and hydroxymethylfurfural; and organic acids including formic acid, acetic acid and levulinic acid; are produced, which have been problematic. Further, since a cellulose-containing biomass contains lignin components, which are aromatic polymers, the lignin components are decomposed during the acid treatment step to produce low molecular aromatic compounds such as phenols as by-products at the same time. These compounds have inhibitory actions during the fermentation step using a microorganism and cause inhibition of the growth of the microorganism, leading to decrease in the yield of the fermentation product. Therefore, these compounds are called fermentation-inhibiting substances and have been seriously problematic when a cellulose-containing biomass sugar liquid was used as a fermentation feedstock.
Examples of the method, which has been disclosed, for removing such fermentation-inhibiting substances during the sugar liquid-producing process include the method called overliming (M. Alfred et al., “Effect of pH, time and temperature of overliming on detoxification of dilute-acid hydrolyzates for fermentation by Saccaromyces cerevisiase,” Process Biochemistry, 38, 515-522 (2002)). In this method, during a step of neutralizing an acid-treated cellulose or saccharified liquid by addition of lime, the liquid is maintained while being heated to about 60° C. for a certain period, to remove fermentation-inhibiting substances such as furfural and HMF together with the gypsum component. However, overliming has only a small effect of removing organic acids such as formic acid, acetic acid and levulinic acid, which has been problematic.
Further, as another method for removing fermentation-inhibiting substances, a method wherein water vapor is blown into a sugar liquid prepared from a cellulose-containing biomass to remove fermentation-inhibiting substances by evaporation has been disclosed (JP 2004-187650 A). However, since such a method by evaporative removal is dependent on the boiling points of the fermentation-inhibiting substances, the removal efficiencies of fermentation-inhibiting substances such as organic acids having low boiling points are especially low, so that a large amount of energy is required to obtain sufficient removal efficiencies, which has been problematic.
There is also a method wherein fermentation-inhibiting substances are removed by ion exchange (Japanese Translated PCT Patent Application Laid-open No. 2001-511418), but it has been problematic in view of the cost. Further, there is a method wherein adsorptive removal is carried out using a wood-based carbide, that is, active carbon or the like, but the subjects to be removed are limited to hydrophobic compounds, which has been problematic (JP 2005-270056 A).